Known fuel filter systems include a housing and a filter element contained therein. Unfiltered fuel is pumped or sucked into the housing via a fuel inlet and exits through a fuel outlet once it has passed through the filter element. The filter element typically includes a ‘dirty fuel side’ where the unfiltered fuel enters the housing and ‘clean fuel side’ where the filtered fuel exits the housing. All the impurities which are separated from the fuel remain trapped in the dirty fuel side of the housing until the housing is emptied.
A disadvantage of this system is that the efficiency of the filter is reduced by any air trapped in the fuel filter after servicing or accumulated during the running of the fuel system. Air may accumulate in the ‘dirty fuel side’ of the system during running, when the filter element becomes wet because it acts as a barrier and any air which is contained in the unfiltered fuel is prevented from passing through the wetted filter element pores. Hence the air is left behind with the impurities trapped in the housing. This accumulated air takes up space which could potentially be used to contain filtered impurities or unfiltered fuel instead. The amount of space taken up by the accumulated air may reach up to 80% of the filter volume on the ‘dirty fuel side’. Hence, this reduces the volumetric efficiency of the filter system and may also increase the frequency in which the filter element must be serviced.
One method of releasing trapped air from a housing is to purge the air back into the filtered fuel outlet line. However, in doing this, there is a risk that as the level of the unfiltered fuel contained within the housing rises, the unfiltered fuel may also pass into the filtered fuel outlet line, which would result in the unfiltered fuel bypassing the filter element and contaminating the fuel system. If the unfiltered fuel then passes into the fuel injector gallery, this may affect the performance of the engine.
The present invention has been made, at least in part, in consideration of the problems and drawbacks of conventional systems.